1. Field of the Invention
One or more embodiments of the present invention relate to a light emitting diode (LED) dimmer circuit for dimming, in accordance with a control signal, an LED illuminated by an alternating current (AC) power source.
2. Background Art
Heretofore, triode for alternating current (TRIAC) dimmers were used for adjusting the brightness of illuminating lamps. The TRIAC dimmer gates the AC waveform, such as from a common commercial 100V AC power source, at a proportion according to a control signal, which is input such as from a switch, and outputs a TRIAC pulse having part of the waveform missing. Therefore, by directly applying the TRIAC pulse to a light bulb, for example, the brightness of the light bulb can be controlled to a brightness corresponding to the control signal.
The TRIAC dimmer is widely common since dimming can be performed with a relatively simple configuration. On the other hand, as LEDs (Light Emitting Diode) have become to be utilized for lighting, the TRIAC dimmer is also used in the dimming for LEDs.
An example is disclosed in Japanese Patent Laid-Open Publication No. 2010-198943.
Furthermore, instead of the TRIAC dimmer, pulse width modulation (PWM) control of LEDs is also known.
Here, compared to a light bulb, for example, an LED has higher sensitivity with respect to current. Thus, when the TRIAC pulse from a TRIAC dimmer is not stable (for example, when the pulse voltage is different at every half period of the alternating current (AC)), flickering appears in the LED. In particular, when the conduction angle of the TRIAC pulse is narrow, flickering is likely to appear. Furthermore, in the case of PWM control, flickering appears if the PWM frequency is low.